This invention relates to contact lenses, and in particular to rigid or hard contact lens having an exceptional combination of oxygen permeability, strength, and resistance to protein and mucus deposits.
There is a great need for a contact lens that has high oxygen permeability, wettability and resistance to protein and mucus deposits. These properties all contribute to an extension of the time during which a contact lens can be continuously worn by a wearer. High oxygen permeability is needed because the pupil of the eye has no blood circulation and extracts the oxygen needed by its cells directly from the atmosphere. Wettability is essential for wearer comfort. Resistance to protein and mucus deposits from fluids that bathe the outer surface of the eye is essential since without this property the deposits will irritate the cornea and in some severe cases the deposits will scratch the cornea surface. Also as a result of the deposits, both visual acuity and the oxygen permeability of the lens can suffer.
Many types of contact lens compositions have been proposed. There are two general categories of contact lenses--rigid and hydrogel. For example, U.S. Pat. Nos. 3,808,178 and 4,120,570 to Gaylord; 4,139,692 to Tanaka et al; 4,686,276 to Ellis et al; 4,743,106 to Novicky et al and to Chen 4,812,598 propose the use of various copolymer compositions including silicon in contact lenses. U.S. Pat. No. 4,130,706 to Plambeck, Jr. proposes a methacrylate-type fluoropolymer ("FMA") for making contact lenses. While the lenses are described as hydrophilic and oxygen permeable, it is believed that they are not wettable enough to be truly comfortable to persons wearing the lenses and are not sufficiently permeable to oxygen to be worn safely and continuously for extended periods. U.S. Pat. No. 3,940,207 to Barkdoll proposes contact lenses constructed of fluorine-containing polymers that are soft and have a low refractive index. It is believed that these contact lenses are not sufficiently oxygen permeable to be worn safely for extended periods.
It would be highly desirable to provide a copolymer which can be used to form a rigid contact lens having the combination of oxygen permeability, wettability and resistance to protein and mucus deposits and having the ability to correct for astigmatism.